This invention relates to the storage of fluids, and more particularly to wheeled vehicles for transporting different liquids in a given container.
When a tank truck or a railroad tank car transporting a particular gas or liquid is to be used to transport a different non-compatible fluid, it is necessary to clean the container of the vehicle. This is usually expensive and inconvenient, and the required specialized cleaning facilities frequently are not available. To solve this problem, it has been proposed that vehicles for transporting fluids be provided with a pair of separate inlets and outlets and a flexible diaphragm that alternately lines opposed sides of the vehicle's container. Movement of the diaphragm to line one side of the container provides a chamber for one fluid, and movement of the diaphragm to the opposite side of the container provides a chamber for a different non-compatible fluid. Thus, the container does not have to be cleaned to enable the vehicle to transport either of such fluids. However, there has not been any significant use of such vehicles having a diaphragm that enables them to alternately carry non-compatible fluids without being cleaned in between. One reason such vehicles have not been used has been the lack of a satisfactory clamping arrangement for preventing leakage of a fluid between the diaphragms and container and for ensuring that the diaphragm will not tear or be pulled loose from the container.
In particular, the diaphragm must be able to resist being pulled out or torn and must not permit leakage during localized transient pressure surges that occur when a vehicle stops, starts or changes direction or speed suddenly. Such movements cause liquid in the vehicle to surge toward its end and may locally trap and compress gas. This can cause the portion of the diaphragm being clamped to be subjected to a localized transient increase in pressure (e.g. 250 p.s.i. for 2 mili-seconds). Although the pressure quickly returns to normal as the liquid surge subsides, any leakage under or through the diaphragm or its clamp which occurs as a result of such a surge necessitates that the container be cleaned before a different liquid can be transported.